The present invention relates generally to tools for measuring electrocardiogram tracings and determining various physiological information therefrom.
Electrocardiogram tracings are graphic representations of electromotive forces generated within the heart of a patient, which electromotive forces are transmitted across the chest wall and sensed by electrodes fixed to the patient""s body. The standard electrocardiogram tracing displays these electromotive forces using Cartesian graphing, where the vertical axis represents the strength of the electromotive force, and the horizontal axis represents the duration of the electromotive force (i.e., the time during which the force is measured). From this graphical information a physician can determine numerous physiological data, including the patient""s heart rate, axis deviations of the electrical axis of the heart, hypertrophy of chambers, conduction abnormalities, etc.
In most instances, electrocardiogram tracings are printed on graph paper comprising numerous minute boxes or squares. The common means of obtaining information from these tracings therefor consists of manually counting these boxes or squares, for instance with a common caliper or compass, a stylus, or other pointing implement. The measurements so obtained can then be input into known formulas for manual calculation of desired physiological data, including, for example, the QTc interval. However, this system is prone to inaccuracies and, thus, the production of flawed measurements and data.
Though the foregoing method is most commonly employed even today, prior art devices have attempted to overcome its inherent drawbacks. Orejola, U.S. Pat. No. 4,388,759, teaches an electrocardiogram caliper for reading electrocardiogram tracings. The caliper is entirely manual, operating much like a slide-rule; one arm of the caliper is calibrated for both amplitude in millivolts and duration of tracing deflections, while the other arm is calibrated for deflection frequency. Each arm further includes a predetermined index line for indexing against the calibrated scale on the opposite arm to thereby determine the values for the measurement made between the arms on the tracing. While an improvement over the unaided counting method described above, the Orejola device is still time-consuming to use, and suffers from an inability to provide more data by the physical limitations of space on the caliper.
A further electrocardiogram measuring device comprising a multi-legged caliper is disclosed in Grayzel, U.S. Pat. No. 5,174,040. That caliper includes a plurality of first parallel members pivotally connected to a plurality of second parallel members in a lattice-like arrangement. The first parallel members include points for aligning with cardiac events on the electrocardiogram tracing, while pivot points associated with the opposite ends of the parallel members are positionable along a predetermined scale calibrated to indicate various physiological data. Like the Orejola device, the Grayzel caliper suffers from an inability to provide more data by the physical limitations of space on the caliper, while its means of operation permits for providing no more than the most basic information from an electrocardiogram tracing.
A final device, taught in Imran, U.S. Pat. No. 4,794,393, comprises an electrocardiogram-tracing measuring device having first and second conductor-carrying members mounted for relative movement. A dielectric covering the conductors permits at least three capacitors to be formed in serial fashion upon relative movement of the first and second members. Electronics coupled to the capacitor translate this relative movement into information corresponding to the electrocardiogram tracing; specifically, milliseconds and beats-per-minute data. The Imran device unfortunately provides only the most fundamental data, and is further limited to measurements taken along the horizontal axis of the electrocardiogram tracing.
It would consequently be desirable to provide an electrocardiogram measuring device that overcomes the problems and disadvantages associated with the prior art.
The present invention addresses and solves the problems discussed above, and encompass other features and advantages, by providing a compass for measuring parameters on an electrocardiogram tracing, and determining physiological information therefrom. The compass comprises a compass body, display screen, and compass legs pivotally connected to the compass body. Means are provided for translating relative movement of the compass legs into electronic signal information corresponding to the distance between the compass legs, which distance in turn corresponds to a measurement taken from an electrocardiogram tracing. The compass is further provided with a computer, for instance in the form of a microchip or the like, operatively coupled to the display screen and adapted to receive the electronic signal information, and further operative to convert the electronic signal information into one or more numerical values corresponding to physiological information to be displayed on the display screen. Thus, for example, a measurement of successive heartbeats is converted into beats-per-minute data, based upon known information such as paper speed and the distance units (e.g., millimeters) upon which the electrocardiogram-tracing measurement is taken. Distance in the horizontal plane is converted to information on the duration of an electromotive force (i.e., time), for measurement of intracardiac intervals. Distance in the vertical plane is converted to information on the duration of an electromotive force, reflective of voltage within the myocardium, and may, for example, be reported in millimeters. The compass is further adapted to calculate physiological information comprising at least one unknown value using one or more known formulas based upon one or more measurements taken with the compass, for instance the QTC interval value according to the known formula QTC=QT/{square root over (R-R)}. To this end, the computer includes a memory for storing electronic signal information corresponding to one or more predetermined variables in one or more formulas for calculating physiological information from the electrocardiogram tracing. The computer is programmed with the one or more formulas, and is further operative to calculate the physiological data from the predetermined variables stored in the memory, and to display the physiological data on the display screen. According to a further feature of this invention, the computer may be provided with standard data for comparison with the calculated unknown value or values. For example, the computer may be provided with standard, or normal, QTC interval values for comparison with the calculated unknown QTC interval value.
A power source powers the computer, the computer memory, and the display screen.